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budku007 (396)

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A shell is fired from a gun from the bottom of the hill along it's slope.The slope of the hill is 30 degrees,and angle of the barrel is 60 degrees.The initial velocity u of the shell is 21m/s.Find the distance along the slope from the gun to the point at which shell falls,take g=10m/ssquare

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lokeshsardana (675)

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is angle 60 degree is with slope or with horizontal

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haseeb2009 (47)

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let angle of slope = @
let angle of projection = #

then range is
=

-2(u)^2cos#sin(# - @)
---------------------------
g cos@
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rhd92781 (686)

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eqn of projectile motion y=xtanw-gx^2/2u^2cos^2w (w is angle o pr)
putting g=10, u=21, w=60 dg
y=rt(3)x-20x^2/441 (i)
eqn of hill's slope is y=xtan30 or y=x/rt(3) (ii)
solving eqns (i) n (ii)
x=441/10rt(3) and y=441/30 coordinates of point where shell falls
dist frm hills bottom = rt(x^2+y^2)
=441/15


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lokeshsardana (675)

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Is it 14.7 m?

my future signature:
LOKESH SARDANA,
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Indian Institute of Technology,Roorkee.


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There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
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budku007 (396)

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rhd is right
 

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spideyunlimited (3081)

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Simple question really... consider the slope of the hill to be as x axis ( tilt the axes)
now in normal equations of projectile motion. substitute g for gcos@ where @ is the angle of the barrel wrt the slope. and of course where theta comes normally u have to take the angle between gun and slope...

in this question u need range so apply range formula.
R = u^2. sin2@ / g
angle between gun and slope is 30 degrees = @
g--> g cos @
So
R = (21)^2 . sin60 / g cos@
R = 441 root(3) / (2 * 10 * root(3) / 2 )
R = 441 / 10
R = 44.1 m along the slope

see how easy it is now :D

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budku007 (396)

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Sorry Spidey u r wrong,I also got the same answer,but rhd's answer is rite

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Anyone who has never made a mistake has never tried anything new
You can never solve a problem on the level on which it was created.
When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity

Purpose of solving a problem is not simply to get the answer(the answer is only an evidence) but to develop your thinking ability
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rhd92781 (686)

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if u've not got it, here's it is:
 
consider the foot of hill on gun's side as origin
slope of hill's surface = 30deg
so its eqn is y=xtan30
or y=x/[ ]3                                                             ....(i)
 
now consider the trajectory of projectile
its eqn is
y=xtan - gx2/2u2cos2
 
now put the values of g=10, u=21,  =60 deg (the angle of projection is 60 deg)
 
the eqn becomes
y=3x-20x2/441                                                         ....(ii)
 
the point on the hill where the shell will fall will be the intersection of eqns (i) and (ii)
 
solving both, we get x=441/103 and y=441/30 m
so its distance frm the origin = (x2+y2) 
which u get as 441/15 m


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I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything
I will not refuse to do the something that I can do.
- Edward Everett Hale
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